Project Summary Photothermal ablation (PTA) therapy provides a minimally invasive treatment for inoperable tumors. Nanoparticles such as gold nanostructures, along with strong photothermal coupling effect, have been shown to greatly enhance the efficacy of PTA. On the other hand, currently used PTA has several limitations such as less effectiveness in treating metastatic cancer; non-biodegradability of the nanoparticles, and restrictive transport of nanoparticles into tumor interstitium in a poorly perfused tumor site. The restrictive transport likely results in sublethal dose of heat transfer and may cause tumor recurrence and develop resistance. Hollow CuS nanoparticles (HCuSNPs) belong to a new class of photothermal nanoparticles. As shown in our Preliminary Study, HCuSNPs, in contrast to gold analogs, were biodegradable and eliminated through the kidney. We hypothesize that the HCuSNPs provide advanced multimodality photothermal therapeutic approaches for control of tumor recurrence and metastases. The Specific Aims of this project are: (1) to evaluate metabolism and toxicity of HCuSNPs; (2) to develop HCuSNPs-mediated multistage delivery for cancer photothermal therapy; and (3) to explore HCuSNPs-adjuvant-mediated in situ photoimmunotherapy (ISPI). In Aim 1, we will examine the cellular fate and metabolism of the PEG-HCuSNPs; and analyze single and repeated dose toxicity of the PEG-HCuSNPs. In Aim 2, we will use photoacoustic imaging to analyze the stages of tumor delivery of HCuSNPs in mouse tumor xenograft model; and validate the effect of PTA through the multistage delivery. In Aim 3, we will assess the immune response induced by HCuSNPs-adjuvant-mediated ISPI; and evaluate the local and distal anti-tumor effect. These studies will be performed in xenograft, allograft and spontaneous models of breast cancer. Worldwide, breast cancer is the second most frequently diagnosed malignancy in women. A success in validating the proposed multimodality PTA will provide an important therapeutic strategy not only for primary but also for metastatic breast cancer. Clearly, this technology, in combination with the use of fiberoptics, can be used to treat a broad range of cancers even in deep tissues.